The invention is concerned with apparatus for filtration of fluids and of carrying out chemical or biochemical analyses requiring prior filtration of fluids.
In one of the commonest laboratory techniques a suspension of solid particles in liquid is separated out by filtration. In its simplest form the filtration is brought about by folding a disk of filter paper into a cone, fitting the cone into a rigid conical filter funnel and inserting this in a flask which is the receiver for the filtrate. More complex apparatus may require elaborately constructed filter means, filter supports, vacuum or pressure pumps and valves. After filtration is complete the apparatus is normally readied for re-use by disassembling it and washing or sterilizing the individual parts. The storage or bench space required for adequate numbers of apparatus and the labour required to assemble and wash them can be considerable. Other disadvantages of this common technique are that the apparatus (being often made of glass) is easily broken, it can be knocked over easily, and unless special fume hoods are available volatile solvents may give off flammable or toxic fumes. Labeling on filters or receivers must be carefully removed in order to avoid confusion when the apparatus is re-used. When biological materials are handled inconvenient precautions are needed to prevent airborne microorganisms contaminating the material being filtered.
A frequent hazard experienced by travellers, campers and survivors of earthquakes etc, is the presence of pathogenic microorganisms in the drinking water. These organisms can be removed by filtration. However, it is rarely practicable to carry or store a bulky filtration apparatus. Many instances of illness ensuing from the drinking of contaminated water might be avoided if a lightweight and portable filtration apparatus were available. Occupants of lifeboats to whom only salt water is available would similarly benefit if a lightweight, portable desalination apparatus were available.
A related problem occurs in many procedures for chemical or biological analysis, where it is necessary to filter the fluid sample before adding the test reagents. For example, it may be difficult to measure the acidity of a soil suspension or lake water by means of a colour sensitive indicator unless the sample is first clarified. In addition to the labour required to perform the filtration, labour is also required to make up solutions of the test reagents and dispense them.
I have realized that the weight and the space normally taken up by the components of filter assemblies, the work involved in fitting them together and of cleaning them, and the making up and adding of chemical reagents are major problems to be overcome in many types of filtration work and in providing local supplies of potable water. It is important to the appreciation of my invention to understand that a complete filtration apparatus comprises three functional elements, namely, the filter means itself, and receptacles for both the fluid to be filtered and the filtered fluid (functionally equivalent to the aforementioned funnel and receiver), said receptacles being capable of holding the whole volume of fluid until such time as it is put to further use. Many inventions claimed to be filtration apparati are not, in fact, complete.
Accordingly, my invention provides a lighweight and self-contained preformed filtration apparatus of insignificant volume when not being used, comprising a filtration means such as a paper or cloth or membrane filter, and two sheets of flexible film or one sheet of said film folded double, said components being joined together in such a way that compartments functionally equivalent to the aforementioned funnel or receiver are formed from the film but are connected to one another internally by said filter means.
My invention also provides for said receiver to be formed in such a way that an orifice is available either directly or only after cutting off a piece of the film, or else it contains a drinking tube or straw through which the filtered fluid may be sucked without need to tilt the apparatus. In each of these cases filtrate may be removed without need to first remove the remainder of the suspension being filtered.
My invention also provides for a filtration apparatus in which the fluid may be isolated from aerial contamination by simply folding the flexible top, and which, when in use, may be suspended from its upper end by means of hooks, wires or other suspending means, so that it may conveniently be suspended from a wall-rack at the side of the work area, rather than standing on a bench.
My invention also provides for indicators of various chemical or biochemical properties (for example, pH, Redox value, etc) to be sealed into one or more of the compartments if so desired, so that tests for these properties can be made automatically on the suspension or filtrate.
My invention also provides for a plurality of filtration compartments to be formed together, with successive filter means of different porosities and with different chemical or biochemical test reagents sealed in or between each receiver, so that a liquid poured into the funnel undergoes successive chemical reactions as it passes through the compartments.
Such apparatus for filtration or chemical analysis being made of flexible material can be stored flat in large numbers in a small space, either lying on top of one another, or removably attached to one another as, for example, on a continuous roll from which single units may be removed by tearing along a perforation. Thus it considerably alleviates the bulk and storage problems associated with carrying out large numbers of filtrations. It is important to note that while the funnel and receiver in my apparatus have no internal volume until the apparatus is put into use, these elements are each and individually capable of holding the whole volume of fluid which is to be filtered, and that being flexible they dilate or contract as necessary to accomodate the addition of fluid to the apparatus and the movement of fluid through it as it passes through the filter means under the influence of gravity.
To use the apparatus the funnel compartment is held open, for example, by thumb and forefinger and the fluid to be filtered is poured in. The flat flexible receiver dilates automatically as the filtrate runs into it and the funnel collapses as it empties. In the apparatus for carrying out chemical or biochemical analyses the reagents dissolve in or disperse in the filtrate from each preceeding compartment and yield colours, precipitates or other reactions according to the known laws of science.
The apparatus can be hung in any convenient space by means of a clip, hook or wire, and these may even be fabricated into the apparatus. However, the actual means of suspension is not critical. In addition, the apparatus can be sealed temporarily by folding over the top of the funnel compartment. Thus it conveniently eliminates the possibility of airborne microorganisms contaminating the fluids, or prevents the release of flammable or toxic vapours. After use the apparatus can be discarded, thereby eliminating the need for washing or removing identifying codes.
When said filter means is of a quality such as to remove pathogenic microorganisms or is a membrane impermeable to dissolved salts my invention provides a lightweight and portable source of potable water. For example, it may be carried folded in a backpack then filled with impure water and hung from the frame of a tent. In one embodiment a drinking straw or tube may be sealed into the receiver so that the user can withdraw purified water as necessary.
My invention thus provides a complete filtration apparatus which enables filtrations or analyses to be carried out immediately, without the need to assemble filter paper, funnel and receiver, or to add test reagents, whereas previously these were required to be stored separately and to be brought together before use, and to be washed out again where necessary after the filtration. This simplifies and speeds up the process and can reduce labour costs.